JPH02181608A - Manufacture of rotation detector and rotary disk - Google Patents

Abstract

PURPOSE:To realize a rotation detecting device which has high resolution by utilizing the technique of an optical disk by providing uneven radial slits which are nearly equal in width and nearly as wide as or wider than the beam diameter of a laser beam which irradiates the slits from a photodetector, on one surface of the rotary disk. CONSTITUTION:The slits 22 are projected by forming the recessed and projections which are almost equal in width on one surface of the rotary disk radially to sufficient length. When the rotary disk rotates and the laser beam 15 from the photodetector 10 reaches the position of the border of a recess and a projection of slits 22, reflected light beams are generated by both the recess and projection parts to interfere with each other, so that almost no laser light returns to the photodetector 10. When the laser light beam 15 comes to the center part of the recess or projection part of a slit 22, almost all of the laser beam is reflected by the recess or projection part to return to the photodetector 10. When the rotary disk rotates by one slit, an electric signal of two cycles is obtained and the intervals of the slits 22 are decreased to realize the rotation detector which has extremely high resolution.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a rotation detection device for detecting the position and speed of a rotating body and a rotating disc for controlling the rotation position and speed by an electric motor or the like. Regarding the manufacturing method.

(Prior Art) As a conventionally used rotation detection device, a system called an optical pulse encoder shown in FIG. 5 is typical. The disk 30 is composed of a disk 30 in which rotating slits 31 are recorded in which parts that transmit light and areas that block light are arranged alternately with the same width in the circumferential direction, and a detector 40 that optically reads the rotation of this rotating slit. is coupled to a rotating body (rotation detected body, not shown) whose rotation is to be detected. The detector 40 includes a light source 41 such as a light emitting diode, a fixed detection slit 42, and a phototransistor 43 that converts an optical signal into an electrical signal. When the disk 30 rotates and the transparent parts of the rotating slit 31 and the detection fixed slit 42 match, light from the light source 41 reaches the phototransistor 43, and when the respective transparent parts and blocking parts match, the light source 41
The light from the phototransistor 43 no longer reaches the phototransistor 43.

The movement of the rotating slit recorded on the disk in this manner becomes the intensity of light reaching the phototransistor 43 from the light source 41, which converts it into an electrical signal.

It is called a pulse encoder because it generates a pulse-like electrical signal whose size changes once each time the disk rotates by an amount corresponding to one slit. With this basic configuration, the electrical signal is the same regardless of forward or reverse rotation, so two sets of detectors with fixed detection slits shifted by one slit interval are used to identify the rotation direction. , optical two-phase pulse encoders that can obtain two-phase electrical signals are often used. Further, since a pulse encoder can detect relative position from the number of pulses but cannot detect absolute position, it is equipped with a zero position detector that generates a pulse only once per rotation.

As such a pulse encoder, S is attached to a magnetic disc.
Magnetic pulse encoders are also used that use magnetic slits that record by alternately magnetizing poles and north poles, but optical pulse encoders have fine slits and can produce a large number of pulses per revolution. In other words, resolution can be increased.

(Problem to be solved by the invention) Recently, when driving robots, etc., conventionally the rotation of a servo motor was driven by gear reduction, but the gear is removed and the servo motor is directly driven (direct drive).
It is attracting attention. There is no play due to gears or a decrease in rigidity, allowing for high-precision and fast movement. The servo motor used for such direct drive rotates at a very low speed, and to control the rotation of this motor, a rotation detecting device with high resolution is required compared to a geared type, which corresponds to the speed reduction of the gear.

Even in optical pulse encoders, when the spacing between the slits becomes several tens of μm or less, the influence of light diffraction cannot be ignored, and the spacing between the rotating slit and the fixed detection slit must be very close, making it difficult to use as a rotation detection device. mechanical assembly becomes extremely difficult. The slits are approximately e, ooo with a slit interval of 50 μm as a disk with a diameter of 10 cm.

On the other hand, as a method of recording data at extremely high density using a rotating disk, there is an optical disk method used in CDs (compact discs) for recording music and LDs (laser discs) for recording video. There is a way to be called.

This is a method of optically reading pits recorded on a disc using laser light.

Figure 6 shows the principle of a CD (compact disc). 5
0 is a part of a CD (compact disc) and is shown enlarged. On one side of the transparent plastic disc 51 is a pit 52 with a width of about 0.5 μm and a depth of about 0.
A concave portion of 11 μm is carved (the part that appears to protrude since FIG. 6 is a view from the side opposite to the surface where the pit is present), and a reflective film 53 is attached to the surface thereof. Furthermore, a protective film 54 is attached to the outside thereof. Laser light with a wavelength of 0.78 μm emitted from the laser diode 11 of the photodetector 10 (called an optical pickup) that reads the pits 52 passes through the beam splitter 12, becomes parallel light by the collimator lens 13, and then passes through the objective lens 14. , and the disk is irradiated from the side opposite to the surface where the pit 52 is located. The laser beam is adjusted to be focused at the pit position by an objective lens 14 in the photodetector IO, and the diameter of the laser beam 15 at the pit position is narrowed to about 1.4 μm. This laser light is reflected by a reflective film 53, passes through an objective lens 14 and a collimator lens 13 in a photodetector 10, is directed by a beam splitter 12, is guided to a photodiode 13, and is converted into an electrical signal. If the laser beam hits an area where there are no pits 52, most of the laser beam will be reflected and a large electrical signal will be obtained.

When the laser beam hits the pit 52, the width of the pit is less than half of the beam diameter of the laser beam, so
The laser light reflected from the pit portion and the laser light reflected from outside the pit are combined and returned to the photodetector 10. An optical path difference between the laser beam reflected from the pit portion and the laser beam reflected from outside the pit is twice the depth of the pit. pit 5
The depth of 2 is selected to be 18 times the wavelength of the laser light inside the plastic, so the reflected laser light from the pit and the
The phase is 180° different from that of the reflected laser beam from outside the cut.
Each interferes and cancels out the other. Therefore photodetector 1
The amount of laser light that returns to 0 is greatly reduced, and the electrical signal obtained also becomes small. In this way, the presence or absence of the pit 52 is converted into the magnitude of an electrical signal and read. The pits are arranged one after another on the circumference, and are further arranged in a spiral shape at a pitch (trough pitch) of 1.6 μm in the radial direction, and a very large number of pits are recorded on the disk. Music data is recorded by a combination of the presence or absence of pits and their length, and the music is played back by reading this data. According to the CD (compact disc) standard, the pit length and the length between pits is a minimum of 0.9μ.
m. Therefore, there is a possibility that a maximum of about 170,000 pits can be recorded on the outer circumference of a disk with a diameter of 10 cm.

Using this technology, it is possible to construct a high-resolution rotation detection device, but it requires tracking in the radial direction so that the laser beam accurately hits narrow pits. This method requires a mechanism to move the objective lens in the radial direction, which has the disadvantage of making the structure complicated. Furthermore, since the rotation detector is attached to an electric motor or the like, there is a risk that it will not be able to track due to the effects of vibration, making it difficult to increase reliability.

The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to obtain a rotation detecting device that has high resolution, has a simple structure, and is highly reliable, using optical Blythesph technology.

[Structure of the invention]

(Means for resolving the division report) The present invention consists of a rotating disk in which slits in which concavities and convexities with approximately equal widths are radially recorded on one surface, and a photodetector that reads the slits with a laser beam. configured,
The widths of the concave portions and convex portions forming the slit are approximately equal to or larger than the beam diameter of the laser beam from the photodetector.

(Function) In the rotating disk of the rotation detection device of the present invention, the unevenness forms a slit having only a small width in the circumferential direction but a sufficient length in the radial direction, so that the photodetector There is no need for a tracking function in the radial direction, and there is no fear that tracking will be lost due to vibration or other factors, resulting in reading failures.

Also, when the rotating disk rotates and the laser beam emitted from the photodetector comes to the boundary between the concave and convex portions of the slit, light is reflected from both the concave and convex portions, and each Due to interference, almost no laser light returns to the photodetector.
The electrical signal obtained is also small. On the other hand, when the laser beam reaches the center of the concave or convex part of the slit, most of the laser beam is reflected by either the concave or convex part and returns to the photodetector, resulting in a gain. The electrical signal generated is also large. The spacing between the slits can be made small, and many slits can be recorded.When the rotating disk rotates for one slit, two cycles of electrical signals are obtained, making it possible to realize a rotation detector with extremely high resolution.

(Embodiment) FIG. 1 is a block diagram of a first embodiment of the rotation detection device of the present invention. 10 is a photodetector, and 20 is a rotating disk, which is roughly divided into two parts.

A portion of the rotating disk 20 is shown enlarged for explanation. The photodetector IO has a configuration similar to that of a photodetector (optical pickup) for an optical disc such as a CD (compact disc), and includes a laser diode 11, a beam splitter 12, a collimator lens 13, an objective lens 14, and an objective lens 15.
1 is a laser beam, and 16 is a photodiode.

The rotating disk 20 is connected to a rotating shaft of a rotating detected body (not shown), and rotates as the rotating detected body rotates.

21 is plastic, 22 is a slit, 23 is a reflective film,
24 is a protective film. The slit 22 is radially formed on one surface of the plastic 21 of the rotating disk to a depth of 0.11 μm1.
Concave portions with a width of 1.2 μm and an appropriate length (Fig. 1 is a view from the reflective side of the surface with the slit, so the portion that appears to protrude) are spaced at intervals of 2.6 μm (the remaining convex portions are 1.3 μm).

), and a reflective film 23 is attached to the uneven surface.

Laser light with a wavelength of 0.78 μm emitted from the laser diode 11 of the photodetector lO is transmitted to the beam splitter 12.
The light passes through the collimator lens 13 into parallel light, and then passes through the objective lens 14 and is irradiated onto the rotating disk 20 from the side opposite to the surface where the slit 22 is located.

The laser beam is adjusted by the objective lens 14 so as to be focused at the position of the slit 22, and the diameter of the laser beam 15 at the position of the slit 22 is narrowed to about 1.4 μm. This laser beam is reflected by the reflective film 23, returns to the photodetector lO, passes through the objective lens 14 and the collimator lens 13, and is changed direction by the beam splitter 12.
The light is guided to a photodiode 16 and converted into an electrical signal. When the center of the laser beam 15 is aligned with the boundary between the concave part and the convex part of the slit 22, half of the laser light is reflected by the concave part and the other half is reflected by the convex part, and these two laser beams and The signals are combined and returned to the photodetector 10. An optical path difference between the laser beam reflected from the concave portion and the laser beam reflected from the convex portion is twice the depth of the concave portion. Since the depth of the concave portion is 0.11 μm, which is selected to be 1/4 of the wavelength of the laser beam inside the plastic 21, the laser beam reflected from the concave portion and the laser beam reflected from the convex portion have different phases, and each interfere and cancel each other out. Therefore, the amount of laser light that returns to the photodetector 10 is greatly reduced, and the electric signal obtained from the photodiode 16 is also small. When the centers of the slits 15 and 15 are aligned, the width of the concave and convex portions of the slit is 1.3 μm, which is approximately equal to the beam diameter of the laser beam of 1.4 μm, so most of the laser light is reflected by the concave or convex portions. photodetector
0, and a large electrical signal is obtained from the photodiode 1B. In this way, the unevenness forming the slit 22 can be converted into the magnitude of an electrical signal and read by the photodetector lO. Since there are two boundaries between the concave portion and the convex portion for one set of slits, two strong and weak signals are obtained each time the slit 22 rotates by the slit interval (2.8 μm) due to rotation of the rotating disk 20.

When the beam diameter of the laser beam is 1.4 μm, the rotating disk 2
If the width of the concave and convex portions of the 0 slit is 1.4 μm or more, an electrical signal with a larger amplitude can be obtained from the photodetector IO. However, increasing the width of the convex and concave portions reduces the number of slits that can be carved around the circumference of the rotating disk, making it impossible to achieve high resolution as a rotation detection device. The width of the convex portion and the concave portion is set to 1.3 μm, which is slightly narrower than the beam diameter of the laser beam. Approximately 210,000 slits can be cut into a rotating disk with a diameter of 10 mm, and an electrical signal of approximately 240,000 cycles can be obtained per rotation.

Also, it is difficult to make the slit shape perfectly rectangular as shown in the figure, and the way the laser beam is reflected at the concave and convex portions changes depending on the shape, so when the laser beam hits each position, The magnitude of the electrical signal obtained from the photodetector differs. The magnitude of this electric signal can be made equal by slightly changing the widths of the concave portion and the convex portion.

As described above, according to the embodiments of the present invention, it is possible to obtain a very high-resolution rotation detection device that utilizes the technology of optical discs such as CDs (compact discs) and LDs (laser discs). By using a slit formed by unevenness and a reflective film similar to the pits on an optical disk, there is no need for radial tracking, the structure is simple, and the reliability of the rotation detection device is greatly improved. In addition, by making the widths of the concave and convex portions that form the slit approximately equal, and making the width approximately equal to or wider than the beam diameter of the laser beam, the rotating disk can be rotated by the amount corresponding to one slit from the photodetector. An electric signal whose amplitude greatly changes twice for each rotation is obtained, the slit interval can be reduced to about 2.6 μm, and a rotation detection device with a resolution higher than that of a conventional optical pulse encoder by an order of magnitude or more can be obtained.

FIG. 2 is a block diagram of a second embodiment of the present invention.

10 is a photodetector, and 20 is a rotating disk. photodetector l
O is the same as in the first embodiment shown in FIG.

The rotating disk 20 has the same structure as the first embodiment, but a slit 22 is formed by forming a radial "convex" on one surface of the plastic 21 of the rotating disk with an appropriate length of 0.11 μm in height and 1.3 μm in width. (Figure 2 is a view from the opposite side of the surface with the slit, so the part that appears concave) is spaced 2.8 μm apart.
(The remaining convex portion is 1.8 μm.) and is made by attaching a reflective film 23 to the uneven surface. Although the method of making the slits in the rotating disk is different, the width of the unevenness is 1.3 μm, and the effect is exactly the same as in the first embodiment.
Effects can be obtained.

In addition, as an example of the present invention, an example of the same configuration as a CD (compact disc) or LD (laser disc), in which a rotating disk is carved with unevenness on a transparent plastic and a reflective film is attached to the surface, was explained. It is also possible to create a structure in which unevenness is carved into the disk to directly reflect the light. In addition, the laser beam is transmitted through the rotating disk without a reflective film, and the unevenness (difference in thickness) carved into the rotating disk changes the phase of the transmitted laser beam and causes interference. The structure may be such that a photodetector reads the intensity of the transmitted laser beam.

To manufacture the rotating disk of the rotation detector of the present invention, a CD (compact disk) or an LD (laser disk) is used.
Almost the same method can be used to produce . For CDs (compact discs), the master disc is first created. Apply photoresist material to a uniform thickness on a disk made of glass or the like with a polished surface, and while rotating the disk, apply a photoresist material of 0.5 μm.
A laser beam focused by a lens is intermittently irradiated depending on the pit pattern to be recorded. At the same time,
The laser beam is moved in the radial direction at a rate of a radial pit pitch (track pitch) of 1.8 am per rotation of the disk. A pit pattern is etched into the photoresist material of the disk as an exposure trace. When this is developed, the photoresist material in the portions corresponding to the pits is removed, the pits appear as recesses, and the master is completed.

After plating this master with a metal such as nickel, the master is removed and a mold (stamper) of the master is made. Using this mold (stambar), plastic is molded by injection molding to create a replica with the same unevenness as the original. A reflective film is applied to this uneven surface by vapor-depositing aluminum or other material. A plastic protective film is then added to create a CD (compact disc).

To make the master disc of the rotating disc of the present invention, a disc made of glass or the like with a polished surface coated with a photoresist material to a uniform thickness is intermittently irradiated with a laser beam at a constant frequency. The rotational speed obtained by dividing this intermittent frequency is controlled to synchronize the intermittent frequency of the laser beam and the rotational speed of the disk. The movement of the laser beam in the radial direction is very small (about 0.1 μm). Therefore, the circumference of the disk is irradiated with a laser beam of a certain number at regular intervals depending on the ratio of the intermittent frequency and the number of rotations, and when the disk rotates once, a small amount (0.1 μm) in the radial direction is irradiated at almost the same position.
The beam is irradiated at a position shifted by a certain amount (degree). Since this radial deviation is small compared to the laser beam diameter (about 0.5 μm), the discs are connected in the radial direction, and by repeating this process, radial slits are carved in the center of the disk as exposure traces. The width of the slit can be controlled by controlling the intermittent time of the laser light beam. By developing this, a master disk having slits formed by unevenness is completed. By changing the characteristics of the photoresist material (negative or positive), the relationship between the concave and convex surfaces can be reversed.

Based on this master disk, it is possible to manufacture rotating disks for the rotation detection device in large quantities at low cost by making copies in the same way as CDs (compact disks).

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a rotation detecting device with extremely high resolution and high reliability, which utilizes the technology of optical discs such as CDs (compact discs) and LDs (laser discs).

There is no longer a need for radial tracking, which was necessary for optical discs, the structure is simplified, and the reliability of the rotation detection device is greatly improved. In addition, by appropriately selecting the relationship between the width of the concave and convex portions forming the slits and the beam diameter of the laser beam, the amplitude of the electric current changes significantly twice each time the rotating disk rotates by an amount corresponding to the spacing of the slits. Once the signal is obtained, the slit spacing is changed to 2.
．． It can be made as small as about 6 μm, and a resolution that is more than an order of magnitude higher than that of conventional optical pulse encoders can be obtained.

Moreover, most of the basic components of the present invention can be applied to optical disks, and rotating disks can be mass-produced in the same way as optical disks, making it possible to realize a high-resolution, highly reliable, and inexpensive rotation detection device.

Note that, like the conventional optical pulse encoder, it is possible to provide a plurality of photodetectors to generate two-phase pulses or one pulse per rotation.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment of the present invention, and Fig. 3 is a block diagram of a conventional optical rotation detection device (optical pulse encoder). , Figure 4 shows a CD (compact disc) with the technology closest to the present invention.
FIG. 10: Photodetector ll: Laser diode 12
: Beam splitter 13: Collimator lens 14: Objective lens 15: Laser light beam lB:
Photodiode 20: Rotating disc 21; 23: 30: 40 = 42; 50: 51: 53; Plastic reflective film disc detector slit phototransistor for detection CD (compact disc) Plastic 528-bit reflective film 54: Protective film 22 Nislit 24 :Protective film 31 Nisrit 41i Light source agent Patent attorney Nori Chika Ken Yudo Daishimaru Ken 20 Rotating circle 1 - sound C disk diagram 5oco<Coca! -4p procedural amendment (
spontaneous) Heisei

Claims (2)

[Claims] (1) Consisting of a rotating disk with unevenness carved on one surface and a photodetector that reads the unevenness with a laser beam, the unevenness is arranged radially with respect to the center of the disk to form a slit, and The width of the concave portion and the convex portion forming the slit are different, and the narrower width of either the concave portion or the convex portion is narrower than the beam diameter of the laser beam irradiated from the photodetector, and the width of the concave portion or the convex portion is narrower than the beam diameter of the laser beam irradiated from the photodetector. An optical rotation detecting device characterized in that one intensity signal is obtained from a photodetector each time the rotating disk rotates by an amount corresponding to the interval between the slits. (2) In manufacturing a rotating disk having a slit formed by the above-mentioned unevenness, a laser beam is emitted while rotating a disk made of glass or the like with a polished surface coated with a photoresist material to a uniform thickness. irradiate intermittently, set the intermittent frequency to a constant frequency, control the disc to a rotational speed that is a division of the intermittent frequency, synchronize the intermittent frequency of the laser beam beam and the rotational speed of the disc, and at the same time A beam of laser light is slowly moved in the radial direction until the disk is 1
By making the distance traveled during rotation smaller than the beam diameter of the laser beam, the laser beam is irradiated onto the disk at regular intervals a constant number of times determined by the ratio of the intermittent frequency and the number of rotations, and When the disk rotates once, almost the same position but slightly shifted in the radial direction is irradiated, creating a shape that is connected in the radial direction.By repeating this process, radial slits are carved as exposure traces around the center of the disk, and this is A method for manufacturing a rotating disk, characterized in that the rotating disk is manufactured by developing a master disk having slits formed by unevenness, and making a copy based on the master disk.